Summary of Work: 1)Data are being analyzed in a study of lung cancer risk associated with residential radon. We studied 1474 lung cancer cases and 1811 controls from Connecticut, Utah, and southern Idaho. Radon was measured in past and current homes using 12-month -track etch detectors to estimate cumulative exposure since age 25. Although a we could not measure radon in a substantial number of homes, these were largely short-term residences. About 60% of participants had complete radon data for the time period from 25 to 5 year prior to diagnosis or interview. We evaluated methods for imputing missing values and have identified factors that can be used to better predict radon levels. We geocoded all residences to facilitate linkage with geographical databases on factors such as radon levels in groundwater and soil porosity which may, in addition to house characteristics, predict radon in homes. Based on earlier State and Federal surveys, we expected 10% of study homes would have radon values that exceed the EPA action value of 4 pCi/L; only about 4% of study homes exceed this value. Using data on mobility patterns within the home, we calculated time/activity weighted cumulative radon exposure values for study participants. Preliminary results suggest little risk associated with the low exposure levels found in CT and UT. Data will be contributed to a pooled analysis combining data from several North American studies. 2) In our study of childhood leukemia, while there was no overall effect of radon, risk was increased with increasing radon exposure among children over age 2. These results are consistent with an effect of radon but could also be due to unmeasured confounding. Radon exposures were low and increased odds ratios were seen for exposures that are generally considered too low to be associated with increased cancer risk.